1. Field of the Invention
The present invention relates to a CMP conditioner for repairing loading of an polishing pad for a semiconductor substrate and for removing materials which have caused loading of the polishing pad, a method for arranging hard abrasive grains for use in a CMP conditioner, and a process for producing a CMP conditioner. The CMP conditioner is also called “CMP dresser” in the art.
2. Background Art
A polishing method called “CMP (chemical mechanical polishing)” has been proposed for polishing wafers. In CMP, chemical polishing action is superimposed on mechanical polishing action to realize a combination of ensuring of satisfactory removal rate with a defect-free polished object, and CMP has widely been used in the step of finish polishing a silicon wafer.
Further, in recent years, an increase in integration density of devices has led to the necessity of polishing the surface of a wafer or the surface of a semiconductor substrate, comprising an electric conductor/dielectric layer formed on a surface of a wafer, in a predetermined stage for the production of an integrated circuit. The semiconductor substrate is polished to remove surface defects such as high projections, scratches, and roughness. In general, this step is carried out during the formation of various elements and integrated circuits on a wafer. In this polishing step, as with the step of finish polishing a silicon wafer, a combination of a removal rate requirement with a defect-free requirement should be met. The introduction of chemical slurry can realize chemical and mechanical flattening of the surface of a semiconductor with higher polishing/removing speed and a defect-free state.
An example of the CMP step (process) is shown in FIG. 8. In this example, a chemical slurry 101 prepared by suspending, for example, silica particles having a diameter of about 5 to 300 nm in a solution of an alkali, such as caustic soda, ammonia, or amine, to prepare a slurry having a pH value of about 9 to 12 and an polishing pad 102 formed of a polyurethane resin or the like are used. At the time of polishing, a semiconductor substrate 103 is abutted against the polishing pad 102 by applying a suitable pressure while allowing the chemical slurry 101 to flow and spread on the polishing pad 102, and the semiconductor substrate 103 and the polishing pad 102 are rotated relatively to each other as indicated by arrows in the drawing.
The polishing pad 102 is conditioned (dressed) with a CMP conditioner while allowing water or the chemical slurry 101 to flow on the polishing pad 102 to repair loading of the polishing pad 102 and to remove materials which have caused the loading of the polishing pad 102. The conditioning with a CMP conditioner is carried out, either after the completion of polishing of the semiconductor substrate 103, by abutting the CMP conditioner against the polishing pad 102, or, simultaneously with the start of polishing of the semiconductor substrate 103, by abutting the CMP conditioner against the polishing pad 102 at its position different from the position where the semiconductor substrate 103 is abutted against the polishing pad 102.
In the CMP conditioner used in the conventional conditioning (brushing) of the polishing pad, as shown in FIG. 9, diamond grains 202 as hard abrasive grains are evenly distributed, for example, by manually spreading the diamond grains 202 over the surface of a disk-shaped support member 201 and then fixing the diamond grains 202 onto the support member 201.
In this case, however, whatever the diamond grains 202 are spread carefully, the distribution of the diamond grains 202 is disadvantageously such that the diamond grains 202 are sparsely present in some portion and are densely present in another portion. When this conditioner with uneven distribution of the diamond grains 202 is used, abrasive grains contained in the chemical slurry are disadvantageously likely to aggregate in a portion where the diamond grains 202 are densely present. This poses a severe problem that the aggregate of the abrasive grains is adhered to the polishing pad (102 in FIG. 8), and, consequently, microscratches the semiconductor substrate (103 in FIG. 8). Further, uneven distribution of the diamond grains 202 is causative of a difference between conditioners and hinders the development of stable conditioner properties.
Further, in the conventional CMP conditioner, since the slurry cannot be smoothly escaped, significant microscratching occurs. In order to improve the escape of the slurry, as shown in FIG. 14, for example, escape grooves 203 for escaping the chemical slurry 101 are provided in the support member 201. In this case, at the time of polishing, the chemical slurry 101 is escaped through the escape grooves 203. The formation of the escape grooves 203 in the support member 201, however, has a fear of adversely affecting CMP conditioner properties. Further, the formation of the escape grooves requires labor and a lot of time. This incurs increased cost.